The subject matter of this invention is related to the apparatus for dewatering and/or washing pulp and paper stock as disclosed in Seifert et al. U.S. Pat. No. 4,722,793 (hereinafter the '793 patent) and in Gilkey, U.S. Pat. No. 5,133,832. The pulp may be derived primarily from waste paper. The major components of that apparatus are two rolls rotatably mounted in spaced relation on parallel axes. An endless mesh-type or porous or "wire" belt is trained around those rolls in wrapping relation with a substantial portion of their surfaces so that the rolls and belt cooperate to define an open space bounded by the rolls and the opposed upper and lower runs of the belt between the rolls.
A headbox is mounted within this space and includes an outlet which delivers the suspension to be dewatered or washed into the entry zone defined by the portion of the wire approaching one roll and the adjacent portion of the surface of that roll, so that this pulp suspension (sometimes referred to as "stock") is trapped on the inside surface of the wire. The rolls are driven at a sufficiently high speed to develop centrifugal force which causes liquid to be expressed through the wire from the stock layer between the wire and each roll, carrying along with it solid contaminates, including ash and ink particles, small enough to pass through the wire mesh. In addition to the centrifugal action, other dewatering mechanisms are also active. Means are provided for collecting the resulting washed and thickened pulp from the second roll and removing it to one side of the apparatus.
In the '793 patent, the roll adjacent the headbox, which will hereinafter be identified as the "breast" roll, is described as being either a smooth, impervious, solid roll, or a solid roll having indentations in its surface, and specifically with that surface comprising circumferentially arranged grooves separated by circumferential land portions, as also shown in patent '832.
The above identified application Ser. No. 649,232 discloses apparatus of the same general structural and operational characteristics as the apparatus of the '793 patent, but differing therefrom in that either or both of the breast roll and the other roll, hereinafter referred to as the "couch" roll, may be provided with an open surface such that the supply of pulp stock can flow into or out of the space within the roll before collecting on the surface of the wire as it passes around the roll. That application discloses a variety of forms of open faced roll, including one form wherein a support shaft has two or more circular disks mounted thereon in axially spaced relation forming the entire support for the wire on the roll.
Application Ser. No. 649,231 discloses a further development of the concept of the '793 patent wherein a third roll is mounted within the wire loop and is provided with its own headbox for supplying stock to be dewatered on top of the layer of pulp traveling to this third roll from the breast roll so that a second layer of dewatered pulp is formed on the wire for travel to and removal from the wire at the couch roll. That application discloses, inter alia, that the breast roll, and also the third roll, may be provided with helical grooves which spiral in opposite directions from the center of the roll.